Etymology

Secular derives from a Latin word meaning "of the age". The Christiandoctrine that God exists outside time led medieval Western culture to use secular to indicate separation from specifically religious affairs and involvement in temporal ones. This meaning has been extended to mean separation from any religion, regardless of whether it has a similar doctrine.

Definitions

2 : not bound by monastic vows or rules; specifically : of, relating to, or forming clergy not belonging to a religious order or congregation <a secular priest>
3 a : occurring once in an age or a century

The publicuniversity systems of the United Kingdom, Australia, New Zealand, Canada, and Japan are also secular, although some government-funded primary and secondary schools may be religiously aligned in some countries.